MPLS Working Group C. Ramachandran
Internet-Draft Juniper Networks
Updates: 4090 (if approved) I. Minei
Intended status: Standards Track Google, Inc
Expires: February 10, 2019 D. Pacella
Verizon
T. Saad
Cisco Systems Inc.
August 9, 2018
Refresh Interval Independent FRR Facility Protectiondraft-ietf-mpls-ri-rsvp-frr-04
Abstract
RSVP-TE relies on periodic refresh of RSVP messages to synchronize
and maintain the LSP related states along the reserved path. In the
absence of refresh messages, the LSP related states are automatically
deleted. Reliance on periodic refreshes and refresh timeouts are
problematic from the scalability point of view. The number of RSVP-
TE LSPs that a router needs to maintain has been growing in service
provider networks and the implementations should be capable of
handling increase in LSP scale.
RFC 2961 specifies mechanisms to eliminate the reliance on periodic
refresh and refresh timeout of RSVP messages, and enables a router to
increase the message refresh interval to values much longer than the
default 30 seconds defined in RFC 2205. However, the protocol
extensions defined in RFC 4090 for supporting fast reroute (FRR)
using bypass tunnels implicitly rely on short refresh timeouts to
cleanup stale states.
In order to eliminate the reliance on refresh timeouts, the routers
should unambiguously determine when a particular LSP state should be
deleted. Coupling LSP state with the corresponding RSVP-TE signaling
adjacencies as recommended in RFC 8370 will apply in scenarios other
than RFC 4090 FRR using bypass tunnels. In scenarios involving RFC4090 FRR using bypass tunnels, additional explicit tear down messages
are necessary. Refresh-interval Independent RSVP FRR (RI-RSVP-FRR)
extensions specified in this document consists of procedures to
enable LSP state cleanup that are essential in scenarios not covered
by procedures defined in RSVP-TE Scaling Recommendations. Hence,
this document updates the procedures defined in RFC 4090 to support
Refresh-Interval Independent RSVP (RI-RSVP) capability specified in
RFC 8370.
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protection mechanism by making the corresponding procedures refresh-
interval independent.
1.1. Motivation
Standard RSVP [RFC2205] maintains state via the generation of RSVP
Path/Resv refresh messages. Refresh messages are used to both
synchronize state between RSVP neighbors and to recover from lost
RSVP messages. The use of Refresh messages to cover many possible
failures has resulted in a number of operational problems.
- One problem relates to RSVP control plane scaling due to periodic
refreshes of Path and Resv messages, another relates to the
reliability and latency of RSVP signaling.
- An additional problem is the time to clean up the stale state
after a tear message is lost. For more on these problems see
Section 1 of RSVP Refresh Overhead Reduction Extensions [RFC2961].
The problems listed above adversely affect RSVP control plane
scalability and RSVP-TE [RFC3209] inherited these problems from
standard RSVP. Procedures specified in [RFC2961] address the above
mentioned problems by eliminating dependency on refreshes for state
synchronization and for recovering from lost RSVP messages, and by
eliminating dependency on refresh timeout for stale state cleanup.
Implementing these procedures allows implementations to improve RSVP-
TE control plane scalability. For more details on eliminating
dependency on refresh timeout for stale state cleanup, refer to
"Refresh Interval Independent RSVP" section 3 of RSVP-TE Scaling
Techniques [RFC8370].
However, the procedures specified in RSVP-TE Scaling Techniques
[RFC8370] do not fully address stale state cleanup for facility
backup protection [RFC4090], as facility backup protection still
depends on refresh timeouts for stale state cleanup.
The procedures specified in this document, in combination with RSVP-
TE Scaling Techniques [RFC8370], eliminate facility backup protection
dependency on refresh timeouts for stale state cleanup including the
cleanup for facility backup protection. The document hence updates
the semantics of Refresh-Interval Independent RSVP (RI-RSVP)
capability specified in Section 3 of RSVP-TE Scaling Techniques
[RFC8370].
The procedures specified in this document assume reliable delivery of
RSVP messages, as specified in [RFC2961]. Therefore this document
makes support for [RFC2961] a pre-requisite.
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In the topology in Figure 1, consider a large number of LSPs from A
to D transiting B and C. Assume that refresh interval has been
configured to be long of the order of minutes and refresh reduction
extensions are enabled on all routers.
Also assume that node protection has been configured for the LSPs and
the LSPs are protected by each router in the following way
- A has made node protection available using bypass LSP A -> E -> C;
A is the Point of Local Repair (PLR) and C is Node Protecting
Merge Point (NP-MP)
- B has made node protection available using bypass LSP B -> F -> D;
B is the PLR and D is the NP-MP
- C has made link protection available using bypass LSP C -> B -> F
-> D; C is the PLR and D is the Link Protecting Merge Point (LP-
MP)
In the above condition, assume that B-C link fails. The following is
the sequence of events that is expected to occur for all protected
LSPs under normal conditions.
1. B performs local repair and re-directs LSP traffic over the bypass
LSP B -> F -> D.
2. B also creates backup state for the LSP and triggers sending of
backup LSP state to D over the bypass LSP B -> F -> D.
3. D receives backup LSP states and merges the backups with the
protected LSPs.
4. As the link on C, over which the LSP states are refreshed has
failed, C will no longer receive state refreshes. Consequently
the protected LSP states on C will time out and C will send tear
down message for all LSPs. As each router should consider itself
as a Merge Point, C will time out the state only after waiting for
an additional duration equal to refresh timeout.
While the above sequence of events has been described in [RFC4090],
there are a few problems for which no mechanism has been specified
explicitly.
- If the protected LSP on C times out before D receives signaling
for the backup LSP, then D would receive PathTear from C prior to
receiving signaling for the backup LSP, thus resulting in deleting
the LSP state. This would be possible at scale even with default
refresh time.
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- If upon the link failure C is to keep state until its timeout,
then with long refresh interval this may result in a large amount
of stale state on C. Alternatively, if upon the link failure C is
to delete the state and send PathTear to D, this would result in
deleting the state on D, thus deleting the LSP. D needs a
reliable mechanism to determine whether it is MP or not to
overcome this problem.
- If head-end A attempts to tear down LSP after step 1 but before
step 2 of the above sequence, then B may receive the tear down
message before step 2 and delete the LSP state from its state
database. If B deletes its state without informing D, with long
refresh interval this could cause (large) buildup of stale state
on D.
- If B fails to perform local repair in step 1, then B will delete
the LSP state from its state database without informing D. As B
deletes its state without informing D, with long refresh interval
this could cause (large) buildup of stale state on D.
The purpose of this document is to provide solutions to the above
problems which will then make it practical to scale up to a large
number of protected LSPs in the network.
4. Solution Aspects
The solution consists of five parts.
- Utilize MP determination mechanism specified in RSVP-TE Summary
FRR [I-D.ietf-mpls-summary-frr-rsvpte] that enables the PLR to
signal the availability of local protection to the MP. In
addition, introduce PLR and MP procedures to establish Node-ID
based hello session between the PLR and the MP to detect router
failures and to determine capability. See section 4.2 for more
details. This part of the solution re-uses some of the extensions
defined in RSVP-TE Summary FRR [I-D.ietf-mpls-summary-frr-rsvpte]
and RSVP-TE Scaling Techniques [RFC8370], and the subsequent sub-
sections will list the extensions in these drafts that are
utilized in this document.
- Handle upstream link or node failures by cleaning up LSP states if
the node has not found itself as MP through the MP determination
mechanism. See section 4.3 for more details.
- Introduce extensions to enable a router to send tear down message
to the downstream router that enables the receiving router to
conditionally delete its local LSP state. See section 4.4 for
more details.
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- Enhance facility protection by allowing a PLR to directly send
tear down message to MP without requiring the PLR to either have a
working bypass LSP or have already signaled backup LSP state. See
section 4.5 for more details.
- Introduce extensions to enable the above procedures to be backward
compatible with routers along the LSP path running implementation
that do not support these procedures. See section 4.6 for more
details.
4.1. Requirement on RFC 4090 Capable Node to advertise RI-RSVP Capability
A node supporting RFC 4090 facility protection FRR MAY set the RI-
RSVP capability (I bit) defined in Section 3 of RSVP-TE Scaling
Techniques [RFC8370] only if it supports all the extensions specified
in the rest of this document. A node supporting RFC 4090 facility
bypass FRR but not supporting the extensions specified in this
document MUST reset RI-RSVP capability (I bit) in the outgoing Node-
ID based Hello messages. Hence, this document updates RFC 4090 by
defining extensions and additional procedures over facility
protection FRR defined in RFC 4090 in order to advertise RI-RSVP
capability [RFC8370].
4.2. Signaling Handshake between PLR and MP4.2.1. PLR Behavior
As per the procedures specified in RFC 4090, when a protected LSP
comes up and if the "local protection desired" flag is set in the
SESSION_ATTRIBUTE object, each node along the LSP path attempts to
make local protection available for the LSP.
- If the "node protection desired" flag is set, then the node tries
to become a PLR by attempting to create a NP-bypass LSP to the
NNhop node avoiding the Nhop node on protected LSP path. In case
node protection could not be made available, the node attempts to
create a LP-bypass LSP to Nhop node avoiding only the link that
protected LSP takes to reach Nhop
- If the "node protection desired" flag is not set, then the PLR
attempts to create a LP-bypass LSP to Nhop node avoiding the link
that the protected LSP takes to reach Nhop
With regard to the PLR procedures described above and that are
specified in RFC 4090, this document specifies the following
additional procedures to support RI-RSVP defined in RFC 8370.
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- While selecting the destination address of the bypass LSP, the PLR
SHOULD select the router ID of the NNhop or Nhop node from the
Node-ID sub-object included RRO object carried in RESV message.
If the MP has not included Node-ID sub-object in RESV RRO and if
the PLR and the MP are in the same area, then the PLR may utilize
the TED to determine the router ID corresponding to the interface
address included by the MP in the RRO object. If the NP-MP in a
different IGP area has not included Node-ID sub-object in RRO
object, then the PLR SHOULD execute backward compatibility
procedures as if the downstream nodes along the LSP do not support
the extensions defined in the document (see Section 4.6.2.1).
- The PLR SHOULD also include its router ID in a Node-ID sub-object
in RRO object carried in PATH message. While including its router
ID in the Node-ID sub-object carried in the outgoing PATH message,
the PLR MUST include the Node-ID sub-object after including its
IPv4/IPv6 address or unnumbered interface ID sub-object.
- In parallel to the attempt made to create NP-bypass or LP-bypass,
the PLR SHOULD initiate a Node-ID based Hello session to the NNhop
or Nhop node respectively to establish the RSVP-TE signaling
adjacency. This Hello session is used to detect MP node failure
as well as determine the capability of the MP node. If the MP has
set the I-bit in CAPABILITY object [RFC8370] carried in Hello
message corresponding to Node-ID based Hello session, then the PLR
SHOULD conclude that the MP supports refresh-interval independent
FRR procedures defined in this document. If the MP has not sent
Node-ID based Hello messages or has not set the I-bit in
CAPABILITY object [RFC8370], then the PLR SHOULD execute backward
compatibility procedures defined in Section 4.6.2.1 of this
document.
- If the bypass LSP comes up and the PLR has made local protection
available for one or more LSPs, then the PLR SHOULD include B-
SFRR-Ready Extended Association object and triggers PATH message
to be sent for those LSPs. If a B-SFRR-Ready Extended Association
object is included in the PATH message, then the encoding and
ordering rules object specified in RSVP-TE Summary FRR
[I-D.ietf-mpls-summary-frr-rsvpte] MUST be followed.
4.2.2. Remote Signaling Adjacency
A Node-ID based RSVP-TE Hello session is one in which Node-ID is used
in the source and the destination address fields of RSVP Hello
messages [RFC4558]. This document extends Node-ID based RSVP Hello
session to track the state of any RSVP-TE neighbor that is not
directly connected by at least one interface. In order to apply
Node-ID based RSVP-TE Hello session between any two routers that are
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not immediate neighbors, the router that supports the extensions
defined in the document SHOULD set TTL to 255 in all outgoing Node-ID
based Hello messages exchanged between PLR and MP. The default hello
interval for this Node-ID hello session SHOULD be set to the default
specified in RSVP-TE Scaling Techniques [RFC8370].
In the rest of the document the term "signaling adjacency", or
"remote signaling adjacency" refers specifically to the RSVP-TE
signaling adjacency.
4.2.3. MP Behavior
With regard to the MP procedures that are defined in RFC 4090, this
document specifies the following additional procedures to support RI-
RSVP defined in RFC 8370.
Each node along an LSP path supporting the extensions defined in this
document SHOULD also include its router ID in the Node-ID sub-object
in the RRO object carried in the RESV message of the LSPs. If the
PLR has not included Node-ID sub-object in the RRO object carried in
PATH message and if the PLR is in a different IGP area, then the
router SHOULD NOT execute the MP procedures specified in this
document for those LSPs. Instead, the node SHOULD execute backward
compatibility procedures defined in Section 4.6.2.2 as if the
upstream nodes along the LSP do not support the extensions defined in
this document.
The node should determine whether the incoming PATH messages contains
B-SFRR-Ready Extended Association object with the Node-ID address of
the PLR as the source and its own Node-ID as the destination. In
addition the node should determine whether it has an operational
remote Node-ID signaling adjacency with the PLR. If either the PLR
has not included B-SFRR-Ready Extended Association object or if there
is no operational Node-ID signaling adjacency with the PLR or if the
PLR has not advertised RI-RSVP capability in its Node-ID based Hello
messages, then the node SHOULD execute backward compatibility
procedures defined in Section 4.6.2.2.
If a matching B-SFRR-Ready Extended Association object is found in
the PATH message and if there is an operational remote signaling
adjacency with the PLR that has advertised RI-RSVP capability (I-bit)
[RFC8370] in its Node-ID based Hello messages, then the node SHOULD
consider itself as the MP for the corresponding PLR. The matching
and ordering rules for Bypass Summary FRR Extended Association
specified in RSVP-TE Summary FRR [I-D.ietf-mpls-summary-frr-rsvpte]
MUST be followed by implementations supporting this document.
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- If a matching Bypass Summary FRR Extended Association object is
included by the PPhop node of an LSP and if a corresponding Node-
ID signaling adjacency exists with the PPhop node, then the router
SHOULD conclude it is NP-MP.
- If a matching Bypass Summary FRR Extended Association object is
included by the Phop node of an LSP and if a corresponding Node-ID
signaling adjacency exists with the Phop node, then the router
SHOULD conclude it is LP-MP.
4.2.4. "Remote" state on MP
Once a router concludes it is the MP for a PLR running refresh-
interval independent FRR procedures, it SHOULD create a remote path
state for the LSP. The "remote" state is identical to the protected
LSP path state except for the difference in RSVP_HOP object. The
RSVP_HOP object in "remote" Path state contains the address that the
PLR uses to send Node-ID hello messages to MP.
The MP SHOULD consider the "remote" path state automatically deleted
if:
- MP later receives a PATH with no matching B-SFRR-Ready Extended
Association object corresponding to the PLR's IP address contained
in PATH RRO, or
- Node signaling adjacency with PLR goes down, or
- MP receives backup LSP signaling from PLR or
- MP receives PathTear, or
- MP deletes the LSP state on local policy or exception event
Unlike the normal path state that is either locally generated on the
Ingress or created from a PATH message from the Phop node, the
"remote" path state is not signaled explicitly from PLR. The purpose
of "remote" path state is to enable the PLR to explicitly tear down
path and reservation states corresponding to the LSP by sending tear
message for the "remote" path state. Such message tearing down
"remote" path state is called "Remote PathTear".
The scenarios in which "Remote" PathTear is applied are described in
Section 4.5.
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Internet-Draft RI-RSVP FRR Bypass August 20184.3. Impact of Failures on LSP State
This section describes the procedures for routers on the LSP path for
different kinds of failures. The procedures described on detecting
RSVP control plane adjacency failures do not impact the RSVP-TE
graceful restart mechanisms ([RFC3473], [RFC5063]). If the router
executing these procedures act as helper for neighboring router, then
the control plane adjacency will be declared as having failed after
taking into account the grace period extended for neighbor by the
helper.
Immediate node failures are detected from the state of Node-ID hello
sessions established with immediate neighbors. RSVP-TE Scaling
Techniques [RFC8370] recommends each router to establish Node-ID
hello sessions with all its immediate neighbors. PLR or MP node
failure is detected from the state of remote signaling adjacency
established according to Section 4.2.2 of this document.
4.3.1. Non-MP Behavior
When a router detects Phop link or Phop node failure and the router
is not an MP for the LSP, then it SHOULD send Conditional PathTear
(refer to Section 4.4 "Conditional PathTear" below) and delete PSB
and RSB states corresponding to the LSP.
4.3.2. LP-MP Behavior
When the Phop link for an LSP fails on a router that is LP-MP for the
LSP, the LP-MP SHOULD retain PSB and RSB states corresponding to the
LSP till the occurrence of any of the following events.
- Node-ID signaling adjacency with Phop PLR goes down, or
- MP receives normal or "Remote" PathTear for PSB, or
- MP receives ResvTear RSB.
When a router that is LP-MP for an LSP detects Phop node failure from
Node-ID signaling adjacency state, the LP-MP SHOULD send normal
PathTear and delete PSB and RSB states corresponding to the LSP.
4.3.3. NP-MP Behavior
When a router that is NP-MP for an LSP detects Phop link failure, or
Phop node failure from Node-ID signaling adjacency, the router SHOULD
retain PSB and RSB states corresponding to the LSP till the
occurrence of any of the following events.
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- Remote Node-ID signaling adjacency with PPhop PLR goes down, or
- MP receives normal or "Remote" PathTear for PSB, or
- MP receives ResvTear for RSB.
When a router that is NP-MP does not detect Phop link or node
failure, but receives Conditional PathTear from the Phop node, then
the router SHOULD retain PSB and RSB states corresponding to the LSP
till the occurrence of any of the following events.
- Remote Node-ID signaling adjacency with PPhop PLR goes down, or
- MP receives normal or "Remote" PathTear for PSB, or
- MP receives ResvTear for RSB.
Receiving Conditional PathTear from the Phop node will not impact the
"remote" state from the PPhop PLR. Note that Phop node would send
Conditional PathTear if it was not an MP.
In the example topology in Figure 1, assume C & D are NP-MP for PLRs
A & B respectively. Now when A-B link fails, as B is not MP and its
Phop link has failed, B will delete LSP state (this behavior is
required for unprotected LSPs - Section 4.3.1). In the data plane,
that would require B to delete the label forwarding entry
corresponding to the LSP. So if B's downstream nodes C and D
continue to retain state, it would not be correct for D to continue
to assume itself as NP-MP for PLR B.
The mechanism that enables D to stop considering itself as the NP-MP
for B and delete the corresponding "remote" path state is given
below.
1. When C receives Conditional PathTear from B, it decides to retain
LSP state as it is NP-MP of PLR A. C also SHOULD check whether
Phop B had previously signaled availability of node protection.
As B had previously signaled NP availability by including B-SFRR-
Ready Extended Association object, C SHOULD remove the B-SFRR-
Ready Extended Association object containing Association Source
set to B from the PATH message and trigger PATH to D.
2. When D receives triggered PATH, it realizes that it is no longer
the NP-MP for B and so it deletes the corresponding "remote" path
state. D does not propagate PATH further down because the only
change is that the B-SFRR-Ready Extended Association object
corresponding to Association Source B is no longer present in the
PATH message.
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Internet-Draft RI-RSVP FRR Bypass August 20184.3.4. Behavior of a Router that is both LP-MP and NP-MP
A router may be both LP-MP as well as NP-MP at the same time for Phop
and PPhop nodes respectively of an LSP. If Phop link fails on such
node, the node SHOULD retain PSB and RSB states corresponding to the
LSP till the occurrence of any of the following events.
- Both Node-ID signaling adjacencies with Phop and PPhop nodes go
down, or
- MP receives normal or "Remote" PathTear for PSB, or
- MP receives ResvTear for RSB.
If a router that is both LP-MP and NP-MP detects Phop node failure,
then the node SHOULD retain PSB and RSB states corresponding to the
LSP till the occurrence of any of the following events.
- Remote Node-ID signaling adjacency with PPhop PLR goes down, or
- MP receives normal or "Remote" PathTear for PSB, or
- MP receives ResvTear for RSB.
4.4. Conditional Path Tear
In the example provided in the Section 4.3.3, B deletes PSB and RSB
states corresponding to the LSP once B detects its link to Phop went
down as B is not MP. If B were to send PathTear normally, then C
would delete LSP state immediately. In order to avoid this, there
should be some mechanism by which B can indicate to C that B does not
require the receiving node to unconditionally delete the LSP state
immediately. For this, B SHOULD add a new optional object called
CONDITIONS object in PathTear. The new optional object is defined in
Section 4.4.3. If node C also understands the new object, then C
SHOULD delete LSP state only if it is not an NP-MP - in other words C
SHOULD delete LSP state if there is no "remote" PLR path state on C.
4.4.1. Sending Conditional Path Tear
A router that is not an MP for an LSP SHOULD delete PSB and RSB
states corresponding to the LSP if Phop link or Phop Node-ID
signaling adjacency goes down (Section 4.3.1). The router SHOULD
send Conditional PathTear if the following are also true.
- Ingress has requested node protection for the LSP, and
- PathTear is not received from the upstream node
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Internet-Draft RI-RSVP FRR Bypass August 20184.4.2. Processing Conditional Path Tear
When a router that is not an NP-MP receives Conditional PathTear, the
node SHOULD delete PSB and RSB states corresponding to the LSP, and
process Conditional PathTear by considering it as normal PathTear.
Specifically, the node SHOULD NOT propagate Conditional PathTear
downstream but remove the optional object and send normal PathTear
downstream.
When a node that is an NP-MP receives Conditional PathTear, it SHOULD
NOT delete LSP state. The node SHOULD check whether the Phop node
had previously included B-SFRR-Ready Extended Association object in
PATH. If the object had been included previously by the Phop, then
the node processing Conditional PathTear from the Phop SHOULD remove
the corresponding object and trigger PATH downstream.
If Conditional PathTear is received from a neighbor that has not
advertised support (refer to Section 4.6) for the new procedures
defined in this document, then the node SHOULD consider the message
as normal PathTear. The node SHOULD propagate normal PathTear
downstream and delete the LSP state.
4.4.3. CONDITIONS object
As any implementation that does not support Conditional PathTear
SHOULD ignore the new object but process the message as normal
PathTear without generating any error, the Class-Num of the new
object SHOULD be 10bbbbbb where 'b' represents a bit (from
Section 3.10 of [RFC2205]).
The new object is called as "CONDITIONS" object that will specify the
conditions under which default processing rules of the RSVP-TE
message SHOULD be invoked.
The object has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class | C-type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: CONDITIONS Object
Length
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This contains the size of the object in bytes and should be set to
eight.
Class
To be assigned
C-type
1
M bit
If M-bit is set to 1, then the PathTear message SHOULD be
processed based on the condition if the receiver router is a Merge
Point or not.
If M-bit is set to 0, then the PathTear message SHOULD be
processed as normal PathTear message.
4.5. Remote State Teardown
If the Ingress wants to tear down the LSP because of a management
event while the LSP is being locally repaired at a transit PLR, it
would not be desirable to wait till the completion of backup LSP
signaling to perform state cleanup. To enable LSP state cleanup when
the LSP is being locally repaired, the PLR SHOULD send "remote"
PathTear message instructing the MP to delete PSB and RSB states
corresponding to the LSP. The TTL in "remote" PathTear message
SHOULD be set to 255.
Consider node C in example topology (Figure 1) has gone down and B
locally repairs the LSP.
1. Ingress A receives a management event to tear down the LSP.
2. A sends normal PathTear to B.
3. Assume B has not initiated backup signaling for the LSR. To
enable LSP state cleanup, B SHOULD send "remote" PathTear with
destination IP address set to that of D used in Node-ID signaling
adjacency with D, and RSVP_HOP object containing local address
used in Node-ID signaling adjacency.
4. B then deletes PSB and RSB states corresponding to the LSP.
5. On D there would be a remote signaling adjacency with B and so D
SHOULD accept the remote PathTear and delete PSB and RSB states
corresponding to the LSP.
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Internet-Draft RI-RSVP FRR Bypass August 20184.5.1. PLR Behavior on Local Repair Failure
If local repair fails on the PLR after a failure, then this should be
considered as a case for cleaning up LSP state from PLR to the
Egress. PLR would achieve this using "remote" PathTear to clean up
state from MP. If MP has retained state, then it would propagate
PathTear downstream thereby achieving state cleanup. Note that in
the case of link protection, the PathTear would be directed to LP-MP
node IP address rather than the Nhop interface address.
4.5.2. PLR Behavior on Resv RRO Change
When a router that has already made NP available detects a change in
the RRO carried in RESV message, and if the RRO change indicates that
the router's former NP-MP is no longer present in the LSP path, then
the router SHOULD send "Remote" PathTear directly to its former NP-
MP.
In the example topology in Figure 1, assume A has made node
protection available and C has concluded it is the NP-MP for A. When
the B-C link fails then C, implementing the procedure specified in
Section 4.3.4 of this document, will retain state till: remote Node-
ID signaling adjacency with A goes down, or PathTear or ResvTear is
received for PSB or RSB respectively. If B also has made node
protection available, B will eventually complete backup LSP signaling
with its NP-MP D and trigger RESV to A with RRO changed. The new RRO
of the LSP carried in RESV will not contain C. When A processes the
RESV with a new RRO not containing C - its former NP-MP, A SHOULD
send "Remote" PathTear to C. When C receives a "Remote" PathTear for
its PSB state, C will send normal PathTear downstream to D and delete
both PSB and RSB states corresponding to the LSP. As D has already
received backup LSP signaling from B, D will retain control plane and
forwarding states corresponding to the LSP.
4.5.3. LSP Preemption during Local Repair4.5.3.1. Preemption on LP-MP after Phop Link failure
If an LSP is preempted on LP-MP after its Phop or incoming link has
already failed but the backup LSP has not been signaled yet, then the
node SHOULD send normal PathTear and delete both PSB and RSB states
corresponding to the LSP. As the LP-MP has retained LSP state
expecting the PLR to perform backup LSP signaling, preemption would
bring down the LSP and the node would not be LP-MP any more requiring
the node to clean up LSP state.
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If an LSP is preempted on NP-MP after its Phop link has already
failed but the backup LSP has not been signaled yet, then the node
SHOULD send normal PathTear and delete PSB and RSB states
corresponding to the LSP. As the NP-MP has retained LSP state
expecting the PLR to perform backup LSP signaling, preemption would
bring down the LSP and the node would not be NP-MP any more requiring
the node to clean up LSP state.
Consider B-C link goes down on the same example topology (Figure 1).
As C is NP-MP for PLR A, C will retain LSP state.
1. The LSP is preempted on C.
2. C will delete RSB state corresponding to the LSP. But C cannot
send PathErr or ResvTear to PLR A because backup LSP has not been
signaled yet.
3. As the only reason for C having retained state after Phop node
failure was that it was NP-MP, C SHOULD send normal PathTear to D
and delete PSB state also. D would also delete PSB and RSB states
on receiving PathTear from C.
4. B starts backup LSP signaling to D. But as D does not have the
LSP state, it will reject backup LSP PATH and send PathErr to B.
5. B will delete its reservation and send ResvTear to A.
4.6. Backward Compatibility Procedures
The "Refresh interval Independent FRR" or RI-RSVP-FRR referred below
in this section refers to the changes that have been proposed in
previous sections. Any implementation that does not support them has
been termed as "non-RI-RSVP-FRR implementation". The extensions
proposed in RSVP-TE Summary FRR [I-D.ietf-mpls-summary-frr-rsvpte]
are applicable to implementations that do not support RI-RSVP-FRR.
On the other hand, changes proposed relating to LSP state cleanup
namely Conditional and remote PathTear require support from one-hop
and two-hop neighboring nodes along the LSP path. So procedures that
fall under LSP state cleanup category SHOULD be turned on only if all
nodes involved in the node protection FRR i.e. PLR, MP and
intermediate node in the case of NP, support the extensions. Note
that for LSPs requesting only link protection, the PLR and the LP-MP
should support the extensions.
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An implementation supporting the extensions specified in previous
sections (called RI-RSVP-FRR here after) SHOULD set the flag "Refresh
interval Independent RSVP" or RI-RSVP in CAPABILITY object carried in
Hello messages. The RI-RSVP flag is specified in RSVP-TE Scaling
Techniques [RFC8370].
- As nodes supporting the extensions SHOULD initiate Node Hellos
with adjacent nodes, a node on the path of protected LSP can
determine whether its Phop or Nhop neighbor supports RI-RSVP-FRR
enhancements from the Hello messages sent by the neighbor.
- If a node attempts to make node protection available, then the PLR
SHOULD initiate remote Node-ID signaling adjacency with NNhop. If
the NNhop (a) does not reply to remote node Hello message or (b)
does not set RI-RSVP flag in CAPABILITY object carried in its
Node-ID Hello messages, then the PLR can conclude that NNhop does
not support RI-RSVP-FRR extensions.
- If node protection is requested for an LSP and if (a) PPhop node
has not included a matching B-SFRR-Ready Extended Association
object in PATH or (b) PPhop node has not initiated remote node
Hello messages or (c) PPhop node does not set RI-RSVP flag in
CAPABILITY object carried in its Node-ID Hello messages, then the
node SHOULD conclude that the PLR does not support RI-RSVP-FRR
extensions. The details are described in the "Procedures for
backward compatibility" section below.
4.6.2. Procedures for backward compatibility
The procedures defined hereafter are performed on a subset of LSPs
that traverse a node, rather than on all LSPs that traverse a node.
This behavior is required to support backward compatibility for a
subset of LSPs traversing nodes running non-RI-RSVP-FRR
implementations.
4.6.2.1. Lack of support on Downstream Node
The procedures on the downstream direction are as follows.
- If the Nhop does not support the RI-RSVP-FRR extensions, then the
node SHOULD reduce the "refresh period" in TIME_VALUES object
carried in PATH to default short refresh default value.
- If node protection is requested and the NNhop node does not
support the enhancements, then the node SHOULD reduce the "refresh
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period" in TIME_VALUES object carried in PATH to a short refresh
default value.
If the node reduces the refresh time from the above procedures, it
SHOULD also not send remote PathTear or Conditional PathTear
messages.
Consider the example topology in Figure 1. If C does not support the
RI-RSVP-FRR extensions, then:
- A and B SHOULD reduce the refresh time to default value of 30
seconds and trigger PATH
- If B is not an MP and if Phop link of B fails, B cannot send
Conditional PathTear to C but SHOULD time out PSB state from A
normally. This would be accomplished if A would also reduce the
refresh time to default value. So if C does not support the RI-
RSVP-FRR extensions, then Phop B and PPhop A SHOULD reduce refresh
time to a small default value.
4.6.2.2. Lack of support on Upstream Node
The procedures on the upstream direction are as follows.
- If Phop node does not support the RI-RSVP-FRR extensions, then the
node SHOULD reduce the "refresh period" in TIME_VALUES object
carried in RESV to default short refresh time value.
- If node protection is requested and the Phop node does not support
the RI-RSVP-FRR extensions, then the node SHOULD reduce the
"refresh period" in TIME_VALUES object carried in PATH to default
value.
- If node protection is requested and PPhop node does not support
the RI-RSVP-FRR extensions, then the node SHOULD reduce the
"refresh period" in TIME_VALUES object carried in RESV to default
value.
- If the node reduces the refresh time from the above procedures, it
SHOULD also not execute MP procedures specified in Section 4.3 of
this document.
4.6.2.3. Incremental Deployment
The backward compatibility procedures described in the previous sub-
sections imply that a router supporting the RI-RSVP-FRR extensions
specified in this document can apply the procedures specified in the
document either in the downstream or upstream direction of an LSP,
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depending on the capability of the routers downstream or upstream in
the LSP path.
- RI-RSVP-FRR extensions and procedures are enabled for downstream
Path, PathTear and ResvErr messages corresponding to an LSP if
link protection is requested for the LSP and the Nhop node
supports the extensions
- RI-RSVP-FRR extensions and procedures are enabled for downstream
Path, PathTear and ResvErr messages corresponding to an LSP if
node protection is requested for the LSP and both Nhop & NNhop
nodes support the extensions
- RI-RSVP-FRR extensions and procedures are enabled for upstream
PathErr, Resv and ResvTear messages corresponding to an LSP if
link protection is requested for the LSP and the Phop node
supports the extensions
- RI-RSVP-FRR extensions and procedures are enabled for upstream
PathErr, Resv and ResvTear messages corresponding to an LSP if
node protection is requested for the LSP and both Phop and PPhop
nodes support the extensions
For example, if an implementation supporting the RI-RSVP-FRR
extensions specified in this document is deployed on all routers in
particular region of the network and if all the LSPs in the network
request node protection, then the FRR extensions will only be applied
for the LSP segments that traverse the particular region. This will
aid incremental deployment of these extensions and also allow reaping
the benefits of the extensions in portions of the network where it is
supported.
5. Security Considerations
The security considerations pertaining to the original RSVP protocol
[RFC2205], [RFC3209] and [RFC5920] remain relevant.
This document extends the applicability of Node-ID based Hello
session between immediate neighbors. The Node-ID based Hello session
between PLR and NP-MP may require the two routers to exchange Hello
messages with non-immediate neighbor. So, the implementations SHOULD
provide the option to configure Node-ID neighbor specific or global
authentication key to authentication messages received from Node-ID
neighbors. The network administrator MAY utilize this option to
enable RSVP-TE routers to authenticate Node-ID Hello messages
received with TTL greater than 1. Implementations SHOULD also
provide the option to specify a limit on the number of Node-ID based
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Hello sessions that can be established on a router supporting the
extensions defined in this document.
6. IANA Considerations6.1. New Object - CONDITIONS
RSVP Change Guidelines [RFC3936] defines the Class-Number name space
for RSVP objects. The name space is managed by IANA.
IANA registry: RSVP Parameters
Subsection: Class Names, Class Numbers, and Class Types
A new RSVP object using a Class-Number from 128-183 range called the
"CONDITIONS" object is defined in Section 4.4 of this document. The
Class-Number from 128-183 range will be allocated by IANA.
7. Acknowledgements
We are very grateful to Yakov Rekhter for his contributions to the
development of the idea and thorough review of content of the draft.
Thanks to Raveendra Torvi and Yimin Shen for their comments and
inputs.
8. Contributors
Markus Jork
Juniper Networks
Email: mjork@juniper.net
Harish Sitaraman
Juniper Networks
Email: hsitaraman@juniper.net
Vishnu Pavan Beeram
Juniper Networks
Email: vbeeram@juniper.net
Ebben Aries
Juniper Networks
Email: exa@juniper.net
Mike Taillon
Cisco Systems Inc.
Email: mtaillon@cisco.com
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